I don't know whats wrong it was running fine I parked for a couple of hours and it would not turn over. I do have power everything is working... lights, air,ect... but I don't have a clue.
it's a 1992 blazer 159000 mi. 4x4 automatic.

 

Does it click at all when you turn to key to crank? If not do this...smack the starter motor with a hammer,etc. then try to crank it. if it cranks then the motors bad. Also check your terminals at the battery etc,make sure they are clean and not corroded.

 

Edit: Chris answered it pretty much

Also if trying to crank it has no effect on lights, then the problem is in the big cable from battery to starter, or the starter itself, not the battery terminals.

If lights dim a lot.. then check terminals or battery.